While power tongs and the clamping units they employ are useful for making and breaking any threaded pipe connection, the primary commercial application for such devices today is in the drilling of wells.
In the drilling of oil, gas and geothermal wells, strings of drill pipe and other well pipe must be made up as the string is run into the well, and disassembled into individual lengths of pipe (referred to as joints) as the string is withdrawn from the well. The successive joints of well pipe are connected together by screw thread connectors. When the well depth is shallow, making and breaking the threaded connections can be done with relative ease, as by using pipe tongs manipulated by hand. In the case of deep wells, many more joints of pipe are required and it becomes necessary to speed up the making and breaking of the connnections between joints and to minimize manual labor. In all cases, it is desirable, and in the case of a deep well essential, to minimize the time required to accomplish a "trip" of the pipe out of and into the well. Thus, for example, to replace a worn drill bit the entire drill string must be pulled from the drill hole, with each of the many threaded connections being broken as the pipe is pulled, the drill bit then being replaced, and the entire string then being reassembled as the new bit and string are run into the drill hole. Prior art workers have accordingly developed power operated tongs of various kinds and power operated spinners, the power tongs being capable of initially breaking the threaded connections and of final tightening of them, and the power operated spinner serving to rotate the pipe rapidly during final unthreading of initial makeup of the connection.
The power tongs art is highly developed, both conceptually and commercially, as shown for example by the following U.S. Pat. Nos.
2,453,369--Grable et al., PA1 2,544,639--Calhoun, PA1 2,705,614--McKibben et al., PA1 3,308,691--Guier, PA1 3,629,927--Palmer et al., PA1 3,902,385--Haby, PA1 3,961,399--Boyadjieff, PA1 U.S. Pat. No. 4,348,920--Boyadjieff.
In usual form prior-art power tongs employ two sets of clamping jaws so arranged that, when the jaws are open, the jaws can accommodate a threaded pipe connection to be made or broken. Thus, one set of jaws can clamp the box of a pin-and-box connection, the other set of jaws clamping the pin. Power means is provided to operate the jaws to clamp and release the respective parts of the connection. The arrangement is such that, when the jaws are clamped on the parts of the threaded pipe connection, at least one set of jaws can be swung, relative to the other set, about the axis of the threaded connection to make or break the same. In some cases, movement of the jaws to clamp and release is pivotal. In other cases, the jaws are moved rectilinearly toward and away from the threaded pipe connection. In all cases, the two sets of jaws, and any structure associated directly therewith, must present an opening such that, initially spaced from the pipe connection, the jaws can be moved laterally of the pipe until the connection is accommodated by the opening. While it is usual for the two sets of jaws each to engage a different part, e.g., the pin and the box of a conventional drill pipe connector, one or both of the sets of jaws may engage the pipe itself, rather than a part of the threaded connector.
Though such prior-art power tongs have achieved extensive commercial acceptance, particularly for use on well drilling rigs, numerous problems have arisen and there has been a continuing need for improvement. Some of those problems arise from the need to have the power tongs capable of operating on vertical pipe, such as pipe extending into a well, and also upon inclined pipe, such as pipe disposed in the so-called "mousehole" receptacle of a well drilling rig. Another problem is that such tongs tend to be relatively massive, complicated and expensive to manufacture.